3/4" Diameter (19.05 mm) Flow Area: 0.442 sq in Standard Capacity: 6.89 GPM @ 5 ft/s Cold Max: 11.02 GPM @ 8 ft/s

3/4" Pipe Flow Rate & GPM Capacity Calculator

A standard 3/4" inside diameter pipe carries 6.89 GPM (26.06 Liters/min) at standard design velocity (5 ft/s) and up to 11.02 GPM at maximum allowable cold water velocity (8 ft/s). Part of our master Pipe Flow Rate Calculator and Copper Flow Rate suite.

Presets:

Pipe Material Specification

Inside Diameter (ID) Required

Fluid Velocity (v) Required

Desired Flow Rate (Q) Required

Primary Output Unit

Calculated Result

Flow Delivery

Estimated Flow Rate (Q)

6.885 US Gallons / min (GPM)

≈ 26.062 L/min

Your pipe with an internal diameter of 0.750 inches has a cross-sectional area of 0.4418 in² (285.02 mm²). At a fluid velocity of 5.00 ft/s, the volumetric flow rate is 6.885 GPM.

Flow Rate Conversions

US Gallons / min 6.885 GPM

Litres / min 26.062 L/min

Litres / sec 0.4344 L/s

Cubic Feet / min 0.9204 CFM

Cubic Metres / hr 1.564 m³/h

Cubic Metres / sec 4.344e-4 m³/s

Internal Flow Area 0.442 in² (285.0 mm²)

Fluid Velocity 5.00 ft/s (1.52 m/s)

Flow results depend on internal pipe diameter and velocity. For actual installations, consider system head loss and friction fittings.

Hydraulic Capacity Matrix

3/4" Pipe Flow Rate vs. Velocity Chart

Volumetric water flow in US Gallons per Minute (GPM), Liters per Minute, and Liters per Second across fluid velocities (1 to 12 ft/s).

Velocity (ft/s)	Flow Rate (GPM)	Liters / Min (L/min)	Liters / Sec (L/s)	Cubic Ft / Sec (cfs)	Hydraulic Status
1 ft/s	1.38 GPM	5.2 L/min	0.087 L/s	0.0031 cfs	✓ Quiet / Hot Water Safe
2 ft/s	2.75 GPM	10.4 L/min	0.173 L/s	0.0061 cfs	✓ Quiet / Hot Water Safe
3 ft/s	4.13 GPM	15.6 L/min	0.260 L/s	0.0092 cfs	✓ Quiet / Hot Water Safe
4 ft/s	5.51 GPM	20.9 L/min	0.348 L/s	0.0123 cfs	✓ Quiet / Hot Water Safe
5 ft/s	6.88 GPM	26.0 L/min	0.433 L/s	0.0153 cfs	✓ Design Standard (5 ft/s)
6 ft/s	8.26 GPM	31.3 L/min	0.522 L/s	0.0184 cfs	⚠ Cold Water Max (8 ft/s)
7 ft/s	9.64 GPM	36.5 L/min	0.608 L/s	0.0215 cfs	⚠ Cold Water Max (8 ft/s)
8 ft/s	11.02 GPM	41.7 L/min	0.695 L/s	0.0246 cfs	⚠ Cold Water Max (8 ft/s)
10 ft/s	13.77 GPM	52.1 L/min	0.868 L/s	0.0307 cfs	⛔ High Velocity / Erosive
12 ft/s	16.52 GPM	62.5 L/min	1.042 L/s	0.0368 cfs	⛔ High Velocity / Erosive

Mathematical Derivation

How to Calculate 3/4" Pipe Flow Rate

Volumetric continuity equation $Q = A \times v$ applied to circular pipes.

Step 1

Calculate Internal Area ($A$)

Compute circular cross-sectional area in square inches:

A = \pi \times (0.375)^2 = 0.4418 sq in

Step 2

Convert Area to Square Feet

Divide square inches by 144:

A_sqft = 0.4418 / 144 = 0.00307 sq ft

Step 3

Apply Continuity (Q = A × v)

Multiply area by design velocity (v = 5 ft/s):

Q_cfs = 0.00307 \times 5 = 0.0153 cfs

Step 4

Convert CFS to US GPM

Multiply cubic feet per second by 448.831 (GPM conversion factor):

Q_gpm = 0.0153 \times 448.83 = 6.89 GPM

Engineering Guidelines

3/4" Pipe Velocity & Hydraulic Guidelines

Noise thresholds, maximum fixture capacities, and erosion limits.

Design Flow Rate (5 ft/s)
6.89 GPM
26.06 Liters/min

Max Cold Water Flow (8 ft/s)

11.02 GPM

Peak demand limit

Hot Water Limit (4-5 ft/s)

5.51 - 6.89 GPM

CDA erosion threshold

Internal Cross Section

0.442 in²

0.75 inch ID

Common Hydraulic Applications for 3/4" Piping:

Main residential water service feed
Bathroom group supply trunk
Water heater cold feed and hot outlet trunk
Outdoor hose bibb main branch

Trade Hydraulic Advisory: The industry-standard supply trunk diameter capable of supplying 2 to 3 simultaneous fixtures without noticeable pressure drop.

Diameter Navigation

Compare Flow Capacities of Other Pipe Sizes

Explore volumetric GPM capacities across other plumbing supply and main line diameters.

← Smaller Pipe 1/2" Pipe Flow Rate Master Engine Pipe Flow Rate Calculator Larger Pipe → 1" Pipe Flow Rate

Expert FAQ Guide

3/4" Pipe Flow Rate FAQs

Engineering questions and velocity guidelines for 3/4" piping.

3 Questions Answered

Q1 How many GPM flows through a 3/4" water line?

At standard residential velocity (5 ft/s), a 3/4" pipe provides 6.89 GPM (26.06 L/min). At maximum cold water velocity (8 ft/s), it flows up to 11.02 GPM (41.71 L/min).

Q2 How many fixtures can a 3/4" water pipe supply?

A 3/4" pipe can comfortably supply 2 to 3 simultaneous fixtures (e.g., two showers and a washing machine) under standard 50-60 PSI municipal street pressure.

Q3 Why is 3/4" pipe required for tankless water heaters?

Whole-house tankless heaters produce 4.0 to 7.0 GPM of continuous hot water. A 1/2" pipe restricts flow to ~3 GPM, choking the heater, whereas 3/4" pipe provides full rated capacity.

Flow Delivery

Flow Rate Conversions

3/4" Pipe Flow Rate vs. Velocity Chart

How to Calculate 3/4" Pipe Flow Rate

Calculate Internal Area ($A$)

Convert Area to Square Feet

Apply Continuity (Q = A × v)

Convert CFS to US GPM

3/4" Pipe Velocity & Hydraulic Guidelines

Common Hydraulic Applications for 3/4" Piping:

Compare Flow Capacities of Other Pipe Sizes

3/4" Pipe Flow Rate FAQs

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